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Macroendocytosis and endosome processing in snake motor boutons
Article first published online: 25 JUN 2007
The Journal of Physiology
Volume 582, Issue 1, pages 243–262, July 2007
How to Cite
Teng, H., Lin, M. Y. and Wilkinson, R. S. (2007), Macroendocytosis and endosome processing in snake motor boutons. The Journal of Physiology, 582: 243–262. doi: 10.1113/jphysiol.2007.130989
- Issue published online: 25 JUN 2007
- Article first published online: 25 JUN 2007
- (Received 26 February 2007; accepted after revision 1 May 2007; first published online 3 May 2007)
We have examined the processing of endosomes formed by macroendocytosis (ME), or bulk membrane retrieval, in active motor terminal boutons at the snake nerve–muscle synapse. Endocytic probes were imaged at light (FM1–43) and electron (horseradish peroxidase (HRP)) levels over stimulus frequencies representing low, intermediate and high levels of use. Endosomes formed rapidly (1–2 s) at all frequencies, concomitant with clathrin-mediated vesicular endocytosis (CME). Endosomes dissipated rapidly into vesicles (∼10 s). The dissipation rate was not influenced by activity. Many endosomes split into clusters of 2–20 smaller endosomes of varying size. Vesicles budded from these smaller endosomes, from large endosomes that had not undergone fission into smaller ones, and from precursor membrane infoldings that had not yet internalized. In snake, exocytosed vesicular membrane is not competent for reuse until after a delay (> 3 min). We found that time required for endosome processing is not responsible for this delay. Endosome processing might, however, limit availability of some vesicles for release at very high levels of use. Generally, endosome processing paralleled that of vesicles internalized directly from the plasma membrane via CME, regardless of stimulus frequency. There was no evidence for differential recruitment of ME versus CME depending upon level of use.